Fuel tank openings with lids can be used for different purposes, for example, for filling the tank, but in particular for carrying out maintenance work on components situated inside the tank, for example, on liquid level indicators or fuel pumps.
The lid is intended to seal the opening in a reliable manner, even after a lengthy period of operation, and to be easily removable. Irrespective of whether the tank is made of metal or plastic, it has a relatively thin wall, so that there is a risk of the closing force causing deformation of the edge. This leads to leakages. Sealing is a particular problem is these types of closures because light fuels are volatile and, as vapors, can also diffuse through solid bodies such as sealing rings. The available structural height is also limited.